Our theoretical prediction and subsequent analysis of experimental data showed that active particles in the core versus the periphery of a dense 3D active particle aggregate exhibit dramatic variations in the dynamics [1]}, [2]}. Whereas cells near the core are characterized by
subdiffusive glassy dynamics (mean square displacement, \(\Delta (t) \sim t^{\alpha }\)  with \(\alpha < 1\)  ), cells in the
periphery exhibit highly directed superdiffusive motion, \(\Delta (t) \sim t^{\alpha }\)  with \(\alpha > 1\) . Such topological differences in the motion of constituent particles in a dense collection of active particles is reminiscent of the variation in the dynamics of particles between the surface and bulk in glasses [3]}. Here, we address the question of how the emergent spatial heterogeneity in the dynamics of three-dimensional (3D) active particle aggregate determine the surface roughness during aggregate expansion into a highly viscous medium. We observe that the strength of inter-particle adhesive interactions strongly up-regulate the surface roughness of expanding dense 3D active particle aggregates. We show that the uptick in the 3D surface roughness is due to the heterogeneity in the radial displacements of the particles on the surface of the expanding 3D aggregates, driven by the symmetry between radial and transverse motions.
